The present invention relates to a signal combining hybrid circuit, and more particularly to a broadband highly efficient in-phase four-way non-directional signal combiner.
A common practice within the radio frequency component design and manufacturing industry is to cascade identical 2:1 impedance transforming hybrid or combiner circuits to form a four-way combiner. Such designs are disclosed, for example, in U.S. Pat. No. 3,192,490 to Petts and U.S. Pat. No. 4,774,481 to Edwards. These combiners transform the input impedance, commonly 50 ohms, to half the input level, or 25 ohms, at the output of the first stage, and then to one quarter of the input level, or 12.5 ohms, at the sum port of the second stage. Thus, a 4:1 impedance transformer is required at the sum port to bring the impedance back to 50 ohms. Such impedance transformers are undesirable, however, because their use increases overall cost of the combiner, increases overall weight of the combiner, and may degrade performance of the combiner.
In order overcome the disadvantages associated with requiring an impedance transformer, an alternative approach was developed wherein various arrangements of cascaded 2:1 impedance step-up and step-down hybrid two-way combiners are used to create a four-way combiner without the use of additional impedance matching transformers. Examples of such arrangements are disclosed in U.S. Pat. No. 3,413,574 to Schroeder and U.S. Pat. No. 3,317,849 to Smith-Vaniz. However, these designs suffer from disadvantages of their own. One such disadvantage is that the combiners disclosed in these patents are limited in frequency range. Another disadvantage is that the designs are quite complicated, requiring many circuit elements, thereby increasing cost, weight, and losses associated with circuit elements.
What is still needed, therefore, is a non-directional signal combiner which utilizes the inherent impedance transformation characteristics of a hybrid circuit in a four-way combiner, thereby eliminating the need for impedance matching transformers, and wherein the step-up and step-down hybrid circuits are interconnected in a balanced arrangement, thereby eliminating transmission line sections resulting in a shorter signal path with reduced losses from input to output.
An object, therefore, of the present invention is to provide a high power four-way power combiner which is simple in design and has a low production cost.
Another object of the present invention is to provide a high power four-way power combiner having the above characteristics and which employs transmission line sections having the same characteristic impedance to simplify the design and reduce costs of production.
Another object of the present invention is to provide a high power four-way power combiner having the above characteristics and which employs a reduced number of transmission line sections to reduce costs of production, and decrease losses.
An additional object of the present invention is to provide a high power four-way power combiner having the above characteristics and which employs isolating terminations of the same impedance to simplify the design and reduce costs of production.
A further object of the present invention is to provide a high power four-way power combiner having the above characteristics and which employs a reduced number of magnetic cores to simplify the design, reduce costs of production, reduce weight and decrease losses.
Yet another object of the present invention is to provide a high power four-way power combiner having the above characteristics and which can be easily, scaled to suit power requirements from a few watts to several kilowatts.
Still another object of the present invention to provide a high power four-way power combiner having the above characteristics and which employs a relatively short signal path length to reduce losses.
These and other objects of the present invention are achieved by a non-directional signal combiner having first, second, third and fourth transmission lines, each having an inner conductor and an outer conductor, and each having first and second ends. The first ends of the inner conductors of the first, second, third and fourth transmission lines are for receiving input signals and may be connected to a coaxial cable connector, for example. The first ends of the outer conductors of the first, second, third and fourth transmission lines are connected to a ground plane.
The signal combiner also includes fifth and sixth transmission lines, each having an inner conductor and an outer conductor, and each having first and second ends. The first end of the inner conductor of the fifth transmission line is connected to the second end of the inner conductor of the second transmission line, the first end of the inner conductor of the sixth transmission line is connected to the second end of the inner conductor of the third transmission line, the first end of the outer conductor of the fifth transmission line is connected to the second end of the outer conductor of the first transmission line, the first end of the outer conductor of the sixth transmission line is connected to the second end of the outer conductor of the fourth transmission line, and the second ends of the inner conductors of the fifth and sixth transmission lines are connected together to form a signal output, and may be connected to a coaxial cable connection, for example.
Seventh and eighth transmission lines are also included, each having an inner conductor and an outer conductor, and each having first and second ends. The first end of the inner conductor of the seventh transmission line is connected to the second end of the inner conductor of the first transmission line, the first end of the inner conductor of the eighth transmission line is connected to the second end of the inner conductor of the fourth transmission line, the second end of the inner conductor of the seventh transmission line is connected to the second end of the outer conductor of the sixth transmission line, the second end of the inner conductor of the eighth transmission line is connected to the second end of the outer conductor of the fifth transmission line, the first end of the outer conductor of the seventh transmission line is connected to the second end of the outer conductor of the second transmission line, the first end of the outer conductor of the eighth transmission line is connected to the second end of the outer conductor of the third transmission line, and the second ends of the outer conductors of the seventh and eighth transmission lines are connected to the ground plane.
In one embodiment the interconnection between the second end of the outer conductor of the first transmission line and the first end of the outer conductor of the fifth transmission line and the interconnection between the second end of the outer conductor of the fourth transmission line and the first end of the outer conductor of the sixth transmission line are connected to the ground plane. When this is the case, even mode impedance inhibitors are employed on the second, third, fifth, sixth, seventh and eighth transmission lines to inhibit flow of current on the outer surfaces of the outer conductors of the second, third, fifth, sixth, seventh and eighth transmission lines.
In another embodiment, the interconnection between the second end of the outer conductor of the second transmission line and the first end of the outer conductor of the seventh transmission line and the interconnection between the second end of the outer conductor of the third transmission line and the first end of the outer conductor of the eighth transmission line are connected to the ground plane. When this is the case, even mode impedance inhibitors are employed on the first, fourth, fifth and sixth transmission lines to inhibit flow of current on the outer surfaces of the outer conductors of the first, fourth, fifth and sixth transmission lines.
Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.